Defoaming,deaerating,and drainage aid compositions



United States Patent Office US. Cl. 252-358 Claims ABSTRACT OF THE DISCLOSURE Compositions containing finely divided silica, oil, and an alkoxysilicon chloride are useful as defoamers, chemical deaerators, and drainage aids.

This invention relates to chemical compositions comprising a finely divided silica made hydrophobic and capable of forming particularly stable suspensions in oil by reacting the silica with alkoxysilicon chlorides. In addition, the present invention relates to the use of such compositions in preventing or controlling foam in aqueous systems and as chemical deaerators and drainage aids in pulp and paper mills.

Many industrial processes are susceptible to foaming, a result which is generally very troublesome. In the pulp and paper industry, alkaline pulping processes are widely used to convert pulpwood into pulp suitable for the manufacture of paper and paperboard. In these processes, pulpwood chips are cooked with highly alkaline materials in digesters. The spent chemicals, known as black liquor, are separated from the pulp and recycled for further use. This is accomplished by filtering the pulp and thoroughly washing the pulp on rotary vacuum filters known as brown stock washers. The filtrate from these washers contains up to about pct. of solids, has a pH of about 12 to 13, and contains a large amount of tall oil fatty acid soaps. Foaming problems are usually extremely severe during this filtering operation and chemical defoamers have been used extensively to control these forms. In the papermaking industry, for example, foam in the headbox (flow boxes) causes froth spots in the finished paper, foam in the tub sizing bath causes nonuniformity in the application of sizing, and foam in the white Water tank causes overflowing, thus carrying away appreciable quantities of fiber to Waste. In summation, the presence of foam in the papermaking process produces two results-one, an increase in operating costs and, two, an inferior product. Since, as pointed out above, the presence of foam and the troublesome results caused thereby are not limited to papermaking processes, but are common to many other industrial processes, particularly those involving aqueous systems, numerous investigations have been directed to the study of foam and more specifically to methods for its control.

Generally, the methods proposed for controlling foam may be divided into two groups, mechanical and chemical. Chemical type defoamers which have been used include higher alcohols, polyalkylene glycols, fatty acids, fatty acid esters, amines, amides, organic phosphates, metallic soaps, and silicones.

The presence of air and other gases in papermaking stocks is the source of numerous difliculties for the papermaker. Surface foam, formed by the release of entrained air, is an obvious and traditional problem; but more subtle and often more diflicult-to-control problems arise from the air that remains within the stock suspension.

A high air content in the headbox stock can complicate operation and control of the paper machine. When tiny gas bubbles are present in the fiber lumen or when they 3,528,929 Patented Sept. 15,, 1970 become attached to the surface of the fibers, the effective density of the fibers is reduced; and there is a tendency for the stock to float. Such flotation leads to increased flocculation and the formation of stock lumps. These lumps pick up air-floated dirt, pitch, filler, pigments, etc., and frequently accumulate at various places throughout the pulp and paper machine systems, including such critical areas as headboxes. Subsequent release of the lumps will produce spots in the paper and will often cause the sheet to break.

On the wire, the tendency of air-containing stock suspensions to form more stable flocs then deaerated stocks has a detrimental effect on sheet formation. In addition, gas bubbles block the pores in the fiber mat and retard drainage. The reduced drainage rate of stock containing air often makes it necessary to operate at higher consistencies, which is another factor that leads to poor formation.

The combined effects of the air in the stock can result in a lower wet-web strength and an increase in porosity (air permeability), a reduction in smoothness, and a decrease in strength properties of the finished sheet. Another etfect of entrained air is a lower density wet web and a lower density final sheet.

Air in the stock has been shown to be the cause of many other operating problems. Accumulation of pockets of air in the stock-handling system causes irregular surges that upset the normal operation of pumps, flow distributors, and headboxes. Excess quantities of air promote slime and nonmicrobiological deposit formation in the stock and white water systems, and in the stock has been found to be a source of pinholes in the finished paper.

The foregoing operating difliculties caused by the presence of air in the stock have been recognized by papermakers for a long time. Although considerable etfort has been made to overcome the difficulties caused by this factor, the results have been less than satisfactory. For example, mechanical deaeration facilities require large capital investments with no assurance that the difliculties will be overcome. Generally, such deaeration equipment fails to remove sufficient air. In a few mill operations, it has been found that such equipment deaerates the stock completely, a highly undesirable result. The optimum conr dition on most machines seems to be a low, but relatively constant, air content.

Another important factor involving the rate of papermaking on existing paper machines is proper drainage, particularly the rate of water removal on the wet end of the machine. The problem, however, is not simply one of obtaining higher drainage rates, but of finding some way to remove Water while maintaining good sheet formation and optimum paper quality. To the best of our knowledge, none of the compositions or methods suggested heretofore for attaining these objectives have been more than partially successful.

The compositions of our invention can effect the deaeration of papermaking stocks by chemical means and thus provide the papermaker the substantial benefits of deaerated stocks without the necessity for the large capital outlay required for mechanical deaeration facilities. In addition, the same compositions have proved to be effective drainage aids for both Fourdrinier and cylinder paper machines, by producing substantial increases in drainage rates and have enabled greater production on many machines and grades where drainage was a limiting factor.

It is, therefore, a principal object of the present invention to provide a composition which obviates the disadvantages of the prior art compositions.

It is another object of our invention to provide new and novel defoaming compositions which can be formed from materials which are available in large quantities.

It is yet another object of the present invention to provide inexpensive defoaming compositions which have an effectiveness comparable to the more expensive types of defoaming compositions.

Yet another object of our invention is to provide a composition that is effective in deaerating papermaking stocks.

Yet another object of this invention is to provide an effective drainage aid for use in papermaking processes.

These and other objects and advantages of the process and compositions will become apparent as this description proceeds.

To the acocmplishmentof the foregoing and related ends, this invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various Ways in which the principles of the invention may be employed.

In brief, the foregoing objects and advantages are attained by the addition to an aqueous system a composition prepared as follows: A finely divided silica is dispersed into a mixture comprising an oil and alkoxysilicon chlorides. The resulting mixture is then heated under reduced pressure to remove substantially all the hydrogen chloride. Finally, an alkylene oxide may be added to react with any residual hydrogen chloride remaining in the system.

The compositions of the invention may be utilized as such by merely adding a small amount, i.e., from about 1 to about 500 parts per million parts of the aqueous systems in which control of foam, deaeration, or an improvement drainage is desired.

Before proceeding with specific examples illustrating our invention, it may be well to indicate in general the types of compounds useful in the invention.

OIL

In general, suitable oils are those meeting the following criteria: Are insoluble in Water, possess a low-vapor pressure, have a viscosity varying from 20-200 S.U.S. at 100 F., possess a specific gravity of less than one, and are nonreactive in respect to the silica and to the hydrophobing agent. Examples of specific mineral oils which may be used include both parafiinic and naphthenic mineral oils, cutting oils, kerosene, and similar petroleum fractions including food-grade mineral oils and halogenated hydrocarbons. A preferred mineral oil is the product known as mineral seal oil which is defined by R. E. Kirk and D. F. Othmer, Encyclopedia of Chemical Technology, The Interscience Encyclopedia, Inc., New York, N.Y., vol. 10, page 167 (1953), as a straightrun treated petroleum distillate from paraflinic or mixedbased crudes.

Specific gravity42.0 API Flash point, Cleveland open cup-260 F. Boiling range522-612 F. Viscosity39 S.U.S. at 100 F.

Under certain conditions it may be desirable to substitute a synthetic oil for the mineral oil. When this substitution is made, it is generally advisable to select a synthetic oil having physical properties similar to those of the mineral oil replaced. Specific examples of suitable synthetic oils include aliphatic diesters (such as diisooctyl azelate), silicate esters (such as hexa-Z-ethyl butoxy disiloxane), and polyalkylene glycols or their derivatives.

SILICA Suitable types of silica are those of colloidal dimensions including the well known forms of silica such as:

(l) Silica aerogel, usually having an acid pH value, a colloidal silica which may be prepared by displacing the water from a silica hydrogel by a low-boiling watermiscible organic liquid; heating in an autoclave or the like above the critical temperature of the liquid; and then venting the autoclave.

(2) So-called fume silica, a colloidal silica obtained by burning silicon tetrachloride and collecting the resulting silica smoke.

(3) A precipitated silica prepared under conditions which do not permit the formation of a gel structure, but rather cause the flocculation of silica particles into coherent aggregates. Colloidal precipitated silica sold under the trademark QUSO is an example of this type of silica.

(4) Arc silica manufactured by vaporizing pure silica in an arc and condensing the silica as very finely divided particles.

Regardless of which form of silica is used, it must be an active silica containing at least some hydroxyl groups to react with the alkoxysilicon chlorides. We have prepared the compositions described in this invention using a fume silica having a surface area of 200 square meters per gram and a limited number of hydroxyl groups. However, we discovered that the defoaming effectiveness was improved when the silica was allowed to adsorb small amounts of water before being reacted with the alkoxysilicon chlorides.

As to size, the diameter of the average ultimate particle should be less than about 100 millimicrons, preferably less than 50 millimicrons.

ALKOXY SILICON CHLORIDE Suitable alkoxysilicon chlorides have the formula: Cl Si(OR) COMPOSITIONS The amount of the various components making up our defoaming compositions in respect to suitable and preferred quantities in parts by weight are as follows:

Component Suitable Preferred Mineral oil 55-93 69-86 Alkoxys lllcon chloride 4-20 8-16 Silica 3-25 6-15 Alkylene oxide 0. 0 0. 3-1. 0

Among the most effective defoamers described in the chemical and patent literature are the silicones. Silicones are very eificient defoamers, but since these compounds are also very expensive, operating costs will be high in any process using a silicone as the defoamer. Obviously, any procedure reducing the amount of silicone required in a given process to control foam will reduce the amount of silicone used. Boylan in US. Pat. 3,076,768 has proposed to employ a dispersion comprising a hydrophobiccolloidal silica-silicone complex, a surface active agent, and a water-insoluble organic liquid serving as an extender. Although such a defoaming agent reduces costs, the product is not entirely satisfactory. This is true because the presence of a surface active agent in the system tends to stabilize foam, thus decreasing the effectiveness of the silica-silicone complex. Among the compounds used by Boylan to render the silica hydrophobic are organo-silicon halides including alkyl(methyl), aryl(phenyl), alkaryl(tolyl), and aralkyl (phenyl methyl) silicon halides. These organo-silicon halides are capable of reacting with the hydroxyl groups of the silica only by eliminating hydrogen chloride. The amount of hydrogen chloride produced is large in comparison to the amounts liberated in preparing the compositions of our invention. Moreover, an unexpected result was found in the form of a markedly increased stability of silica suspensions prepared with alkoxysilicon chlorides. Such suspensions were much more stable than those prepared by any heretofore known method of making silica hydrophobic. Although the mechanism whereby such unexpected results were achieved is not fully understood, it is believed that it may result at least in part from the reaction of the alkoxyl groups with the hydroxyl groups of the silica and the elimination of water plus the formation of hydrogen bonds between the unreacted hydroxyl groups of the silica and the oxygen atoms of the alkoxyl groups.

Liebling et al. in US. Pat. 3,207,698 teach a process for the production of an antifoam composition whereby the use of a surface active agent is eliminated. These patentees in their process must, however, use a special type of precipitated silica; namely, a silica the particles of which have an average diameter of from 0.005 to 0.050 micron, a surface area of 200 to 400 square meters per gram, and a pH of from 8 to 10. In contrast, we have found that suitable defoaming compositions can be prepared in accordance with our invention with a number of silica products. These silica products may have either an acid or an alkaline pH and may be prepared by precipitation from water, by the oxidation of silicon tetrachloride, or by the vaporization of silica in an arc.

The compositions of our invention obviate the disadvantages of compositions described in various patents by utilizing cheap starting materials, such as alcohols and silicon tetrachloride, eliminating the need for surface active agents, reducing the corrosive nature of the products containing hydrogen chloride, and by utilizing a wide variety of silica products.

In order to disclose the nature of the invention still more clearly, the following illustrative examples will be given. It is understood, however, that the invention is not to be limited to the specific conditions or details set forth in these examples, except insofar as such limitations are specified in the appended claims.

EXAMPLE 1 Preparation of a mixture of bisand tris(decyloxy)silicon chlorides A 2,000-gal. glass-lined reactor was charged with 2,800 lb. (16.48 pound moles) of silicon tetrachloride, which was then agitated and cooled to 50 F. by circulating icewater through the jacket of the reactor. Decyl alcohol was then added to the reactor at the rate of 30 lb. per minute until 7,120 lb. (44.98 pound moles) had been added. During the addition of the decyl alcohol, the temperature was kept at 50 F. or lower and the hydrogen chloride formed was vented to a scrubber. The contents of the reactor were then heated to 200 F., the reactor was sealed and a vacuum was applied to remove additional hydrogen chloride. Upon completion of the reaction, the contents were cooled to less than 100 F. The residual weight of the mixture of bisand tris(decyloxy) silicon chlorides was 8,250 lb. This product contained 8.94 pct. chlorine and 11.80 pct. of silicon calculated as SiO The theoretical chlorine and SiO for the mixture is 8.97 pct. chlorine and 11.94 pct. silicon calculated as SiO EXAMPLE 2 A 2,000-gal. glass-lined reactor was charged with 10,320 lb. of a mineral seal oil and 1,980 lb. of the mixture of bisand tris(decyloxy)silicon chlorides prepared in Example 1. The contents of the reactor were agitated and 1,700 lb. of silica was added slowly to the mixture. This silica had an ultimate particle size of about 13 millimicrons and a pH of 8.5. The reactor was then vented to a scrubber and the contents heated to 200 F. and maintained at this temperature for 1 hr. A 20-25 in. Hg vacuum was applied to the reactor as the batch was cooled to F. The batch was then treated with lb. of butylene oxide and homogenized. The final product contained a total silicon content, calculated as SiO of 12.5 pct. and a defoaming eifectiveness of 89 pct.

EXAMPLE 3 A 250ml. three-necked round bottom flask equipped with a thermometer, reflux condenser, dropping funnel, and a magnetically driven stirring bar was charged with 17.0 g. (0.1 mole) of silicon tetrachloride and cooled to below 20 C. The temperature was maintained below 20 C. while 39.1 g. (0.3 mole) of isooctyl alcohol was added over a period of 2 hr. The reaction mixture was then slowly warmed to 100 C. and a 30-40 mm. Hg vacuum was applied for 1 hr. after which the reaction was cooled. The tris(isooctyloxy)silicon chloride obtained was then reacted with silica as described in Example 4.

The reaction described above was repeated using 0.3 mole quantities of n-butanol, sec-butanol, decyl alcohol, tridecanol, a mixture of C to C straight chain alcohols, a mixture of C to C straight chain alcohols, and a mixture of C to C straight chain alcohols.

EXAMPLE 4 A 250-ml. three-necked flask equipped with agitator and thermometer was charged with 74.0 g. of mineral seal oil, 14.0 g. of the tris(isooctyloxy)silicon chloride prepared in Example 3 and 12.0 g. of a silica having an ultimate particle size of about 13 millimicrons and a pH of 8.5. The mixture was heated to 100 C. and the temperature was maintained at 100 C. for 1 hr. while a vacuum of about 30 mm. Hg was applied to remove hydrogen chloride. The reaction mixture was then cooled to 25 0., treated with 0.1 g. of butylene oxide and homogenized in a Waring Blender for 3 minutes.

The reaction was repeated with the various alkoxysilicon chlorides prepared in Example 3 and the products obtained were tested for defoaming ability. The results obtained were as follows:

Alcohol used to prepare Foam reduction,

The procedure described in Example 4 was used to prepare several compositions from tris(decyloxy)silicon chlo= ride and a variety of silicas. Defoaming abilities were as follow:

Surface area Foam resquare meters duction Silica used per gram pH percent 1 Precipitated silica 300 8. 5 86 2- Silica aerogel 1 110-150 3. 5-4. 0 90 3. do 110-150 3. 5-4. 0 79 4 Fumed $1110 200 3. 5-4. 2 94 5 Arc silica 4.3-4. 7 84 6 do 185 4. 3-4. 7 78 1 Aggregate particle size, 3-5 microns. 2 Aggregate particle size, 0.5-3.0 microns. 3 Arr classified to remove agglomerates.

The defoaming ability of the various compositions prepared in accordance with Examples 2, 4, and 4 was determined as follows: A 0.1 molar tall oil soap solution (stock solution) was prepared by adding sodium hydroxide in an amount equal to 102 pct. of the stoichiometric quantity required for complete neutralization of tall oil fatty acids, followed by diluting the neutralized tall oil fatty acid solution to volume with demineralized water. A working solution was prepared by diluting 25 ml. of the stock solution to 2 liters with demineralized water, allowing the solution to stand for 24 hr. and adjusting the pH to 8.7. Eighty-five milliliters of the Working solution was transferred to a 250-ml. bottle and shaken vigorously for 30 seconds, producing a foam which had a height of approximately 50 mm. After noting the foam height in the bottle, a sufficient quantity of the defoaming composition was added so that the concentration of the defoamer was 100 parts per million parts of the soap solution. The bottle was then shaken vigorously for an additional seconds, the residual foam height was measured and the percent reduction in foam was calculated.

While particular embodiments of the invention have been descirbed, it will be understood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated to cover by the appended claims any such modifications as fall within the true spirit and scope of the invention.

The invention having thus been described, what is claimed and desired to be secured by Letters Patent is:

1. A method of preparing a defoaming composition which comprises dispersing 3 to 25 parts by weight of finely divided silica into a mixture consisting of 55 to 93 parts by weight of a mineral oil or a synthetic oil that is nonreactive in respect to the silica and the hydrophobic agent having a viscosity varying from to 200 S.U. S. at 100 F. and 4 to 20 parts by weight of an alkoxysilicon chloride having the formula:

wherein m varies from 1 to 2, n varies from 2 to 3, and R is a straight or branched chain alkyl group containing from 2 to 22 carbpn atoms; and heating the resulting mixture at a temperature varying from ambient to about 100 C. at a pressure varying from about 20mm. of mercury to about atmospheric until substantially all the hydrogen chloride is removed therefrom.

2. The method of claim 1 wherein the amount of silica varies from 6 to 15 parts by weight, that of the oil varies from 69 to 86 parts by weight, that of the alkoxysilicon chloride varies from 8 to 16 parts by weight.

3. The method of claim 2 wherein the silica is a precipitated silica, the oil is a mineral seal oil, and the alkoxysilicon chloride is a mixture of bisand tris-(decyloxy)silicon chlorides.

4. A defoaming composition prepared by the process of claim 1.

5. A defoaming composition prepared by the process of claim 1 in which the alkoxysilicon chloride is a mixture of bisand tris-(decyloxy)silicon chlorides.

6. A defoaming composition prepared by the process of claim 1 in which the oil is a mineral oil.

7. A defoaming composition prepared by the process of claim 1 in which the oil is a mineral seal oil.

8. A defoaming composition prepared by the process of claim 1 in which the silica is a precipitated silica.

9. A defoaming composition prepared by the process of claim 1 in which the silica is a fume silica prepared by oxidizing silicon tetrachloride.

10. A defoaming composition prepared by the process of claim 1 in which the silica is an arc silica prepared by vaporizing silica in an arc.

References Cited UNITED STATES PATENTS 3,207,698 2/1963 Boylan 252--358 3,076,768 9/1965 Liebling et al. 252-358 2,736,668 2/1956 Broge 117-100 JOHN DAVID WELSH, Primary Examiner US. Cl. X.R. 252318, 321 

